A device for concentrating and recovering target particles using a concentration device in which filtering is combined with ultrasonic trapping after impurities in liquid are removed by no-contact trapping using a standing ultrasonic wave, or a water treatment device reduced in filter clogging frequency, which is particularly effective in detecting microorganisms in water. Specifically, a water treatment device for removing particles in water by a filter, wherein a frequency in maintenance including filter replacing and backwashing can be reduced.
